1. Field of the Invention
The present embodiments relate to a display and a driving method thereof. More particularly, the present embodiments relate to an organic light emitting display and a driving method thereof, which display images of desired luminance.
2. Description of the Related Art
Various flat panel displays are capable of reducing the weight and volume that are disadvantages of cathode ray tubes (CRTs). Flat panel displays include liquid crystal displays (LCDs), field emission displays (FEDs), plasma display panels (PDPs), and organic light emitting diode (OLED) displays.
Among the flat panel displays, the OLED displays employ organic light emitting diodes that emit light by re-combination of electrons and holes. The OLED displays have advantages of high response speed and small power consumption.
FIG. 1 illustrates a view showing a pixel 4 of a related art OLED display.
With reference to FIG. 1, the pixel 4 of the related art OLED display may include an OLED and a pixel circuit 2. The pixel circuit 2 may be connected to a data line Dm and a scan line Sn, and may control the OLED. The pixel circuit 2 may be connected to a first power source ELVDD directly, and to a second power source ELVSS through the OLED.
An anode electrode of the OLED may be connected to the pixel circuit 2, and a cathode electrode of the OLED may be connected to the second power source ELVSS. The OLED may generate light of a predetermined luminance corresponding to an electric current from the pixel circuit 2.
When a scan signal is supplied to the scan line Sn, the pixel circuit 2 may control an amount of an electric current provided to the OLED corresponding to a data signal provided to the data line Dm. To do this, the pixel circuit 2 may include a first transistor M1, a second transistor M2, and a storage capacitor C. The first transistor M1 may be connected between the data line Dm and the scan line Sn. The second transistor M2 may be connected between a first power source ELVDD and the OLED. The storage capacitor C may be connected between a gate electrode and a first electrode of the second transistor M2.
A gate electrode of the first transistor M1 may be connected to the scan line Sn, and a first electrode of the first transistor M1 may be connected to the data line Dm. A second electrode of the first transistor M1 may be connected with one terminal of the storage capacitor C. The first electrode may be set as a source electrode or a drain electrode, and the second electrode may be set as an electrode other than the first electrode. When the first electrode is set as the source electrode, the second electrode may be set as the drain electrode. When a scan is supplied to the first transistor M1 connected with the scan line Sn and the data line Dm, the first transistor M1 may be turned-on to provide a data signal from the data line Dm to the storage capacitor C. At this time, the storage capacitor C may be charged with a voltage corresponding to the data signal.
A gate electrode of the second transistor M2 may be connected to one terminal of the storage capacitor C, and a first electrode of the second transistor M2 may be connected to another terminal of the storage capacitor C and the first power source ELVDD. A second electrode of the second transistor M2 may be connected with the anode electrode of the OLED. The second transistor M2 may control an amount of an electric current flowing from the first power source ELVDD to the second power source ELVSS through the OLED according to the voltage charged in the storage capacitor C. The OLED may emit light corresponding to an amount of an electric current supplied from the second transistor M2.
The pixel 4 of the related art OLED display may display images of desired luminance by repeating the aforementioned procedure. During digital driving in which the second transistor M2 functions as a switch, a voltage of the first power source ELVDD and a voltage of the second power source ELVSS may be supplied to the OLED. The OLED may thus emit light by being driven with a regulated voltage. As time elapses, an internal resistance of the OLED may increase, and a drive current may be reduced to not display images of desired luminance. With sufficient time, the OLED may degrade. When the OLED degrades, the luminance may be reduced, in relation to the same electric current employed previously. This may cause the images of desired luminance not to be displayed.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.